Slice
the beef into 2 mm (1/16 in) strips and combine in a bowl with 2 tablespoons of
the chopped lemon grass, all the fish sauce and half the garlic. Allow the meat
to marinate for 10 minutes.

Add
half the oil to a wok over medium heat and fry half of the onion, half of the
remaining lemon grass and half of the remaining garlic for 1–2 minutes, or
until fragrant. Increase the heat to very high and add half the beef and its
marinade to the wok. Stir-fry for 2 minutes, then remove the beef from the wok.

Repeat
the previous process with the remaining beef, onion, lemon grass and garlic.
Return the first batch of beef to the wok, season with the sugar, salt and
pepper, and continue to stir-fry to heat through. Serve on top of vermicelli
salad.

To
finish, top with the essential fried shallots, peanuts and dipping fish sauce.